Thursday 5th February 2004
I decided to investigate the twitchiness of the robot following the Worthing event. The radio reception of Hog 2 had never been quite as good as Hog 1, but I hadn't as yet figure out why this was. I had recently been on the Technobots website to find that there was a new addition to the technical guides section that talked about interference problems and how to resolve them. Encourage by the very interesting and useful guide notes from Tim Mann, I started to look seriously into my own problem.
The first thing I checked was whether the twitchiness was due to all the power supplies to the controller being generated from my single 24 volt battery supply. I connected an independent set of batteries to the receiver and then turned on the transmitter with the aerial retracted. I didn't have to walk far away from the Hog before the motors twitched. I didn't know if the interference was there all the time or only when a valid radio signal was detected, so I connected a servo to a spare port on the receiver and watched it as I turned the transmitter on and off. I noticed that with the receiver off, and consequently the failsafe relays on the robot turned off, the servo was steady. As soon as I turned the transmitter on and the failsafe relay switched power through to the motors and actuators, it was then that the servo twitched as well as the motors.
I prodded about with the oscilloscope probe for quite a while trying to spot anything obvious, but couldn't see anything. I soldered a few capacitors in strategic places to smooth out power rails, but to no avail. I then, by chance, looked at the input feed to the DC-DC converter that I use to generate a 36v supply to drive the high-side MOSFETs. To my amazement there were horrible 1 volt spikes continuously on the input. This 12 volt input feed to this converter came from a power regulator that I had forgot to smooth out properly with a capacitor, so I quickly soldered a 100uF capacitor across it and checked it again. To my relief it made a world of difference, so I was well chuffed with the stability of the controller by the end of the evening.
Thursday 15th February 2004
On 14th and 15th February I took part in the the Brighton Modelworld exhbition and had a great time. You can read about what happened in the events section.
With the exhbition now over, I had learnt a lot because of the number of battle I had endured. As a result I realised there were a number of improvements that I could make; some as a result of comments made during the tech-check' and others from the battle injuries sustained throughout the event.
The things I think need to concentrate on immediately are:
Gas bottle protection
Gas bottle access flap
More panel fixing bolts
Allen key panel fixing bolts
24volt motors, not over-run
Smaller drive sprockets on wheel axles
I've signed up to go the the Portsmouth exhibition in May, so will have to start on some of these improvements over the coming weeks.
Last updated 9th May